1. Field of the Invention
The present invention relates generally to drive sprockets for tracked vehicles, and relates more specifically to the tooth design for such drive sprockets having improved traction with reduced noise generation.
2. Description of Related Art
Tracked vehicles such as snowmobiles and snow groomers drivingly engage the ground through one or more endless tracks. Endless tracks conventionally include an outer side with a pattern of projecting lugs or ribs that are designed to engage the snow or other ground surface, apply traction, and propel the vehicle. Conventional endless tracks also include an inner side that engages one or more drive sprockets, which, in turn, are operatively connected to a propulsion system of the vehicle.
The drive sprockets and the inner side of the endless track typically include mating teeth that provide traction between the drive sprockets and the endless track. Conventional drive sprockets use either external or internal teeth.
FIGS. 9 and 10 illustrate a drive sprocket 1010 that includes a plurality of radially-extending sprocket teeth 1020 projecting outwardly from an outer circumferential side of the sprocket 1010. An endless track 1030 includes a plurality of longitudinally spaced holes that define a plurality of track teeth 1040. Reinforcing metal bars (not shown) extend laterally across the endless track 1030 through the track teeth 1040 to reinforce the track teeth 1040 and the track 1030. The track teeth 1040 mesh with the sprocket teeth 1020 to provide traction between the drive sprocket(s) 1010 and the track(s) 1030. In the typical example where the drive sprocket 1010 is used, two such sprockets 1010 usually are provided to engage each endless track 1030.
Each track tooth 1040 is surrounded by a metal alignment cleat 1050 that meshes with the sprocket 1010 to keep the endless track 1030 laterally aligned with the drive sprockets 1010. As the drive sprockets 1010 rotate to propel the vehicle, the cleats 1050 rattle against the valleys formed between adjacent sprocket teeth 1020. This metal-to-metal contact creates noise, especially when the vehicle travels quickly.
FIGS. 11–13 illustrate an additional conventional drive sprocket 1060 that includes a plurality of axially-extending sprocket teeth 1070. An endless track 1080 includes a plurality of longitudinally-spaced track teeth 1090 projecting inwardly from an inner side of the endless track 1080. The sprocket teeth 1070 engage the track teeth 1090 to provide traction between the sprocket 1060 and the endless track 1080. Alignment cleats 1050 are laterally offset from the track teeth 1090 on the endless track 1080 and the sprocket teeth 1070. Consequently, the cleats 1050 do not typically rattle against the sprockets 1060 as much as in the previous example, and noise is reduced as compared to sprockets 1010 that rely on radially-extending teeth 1020.
While the use of axially-extending teeth 1070 instead of radially-extending teeth 1020 reduces noise, the axially-extending teeth 1070 are not as effective at generating traction with the track 1080 as the radially-extending teeth 1020. The reduction in traction may be caused, in part, by the fact that the internal track teeth 1090 are typically not reinforced and therefore deform under high loads. Accordingly, a greater number of sprockets 1060 must be used to generate sufficient traction with the endless track 1080. As illustrated in FIGS. 8 and 9, four internally toothed sprockets 1060 (two inner sprockets 1060 with two sets of sprocket teeth 1070 and two outer sprockets 1060 with one set of sprocket teeth 1070) are typically used.
As a result of this, a need has developed for a sprocket construction that provides the superior traction of the drive sprocket 1010 while also minimizing the generation of noise as does the drive sprocket 1030.
Others have attempted to solve these problems. FIGS. 14–16 illustrate an additional conventional drive sprocket 1110 that includes a plurality of axially-extending sprocket teeth 1120. The sprocket teeth 1120 engage the track teeth 1090 of the endless track 1080, as shown, for example, in FIGS. 12 and 13. The drive sprocket 1110 further includes a plurality of radially-extending sprocket teeth 1130 projecting outwardly from the an outer circumferential side of the sprocket 1110. The radially-extending sprocket teeth 1130 mesh with track teeth 1040, as shown, for example in FIGS. 9 and 10 to provide traction between the drive sprocket 1110 and the endless track. The radially-extending sprocket teeth 1130 extend directly from the outer circumference of the sprocket 1110 and have a width substantially the same as the sprocket teeth 1120. The drive sprocket 1110 exhibits many of the drawbacks identified above.